Paintball guns are great, but they make a big mess, what with all that paint. And water guns are great, but you don't get the satisfaction of shooting bullets. Well, this gun fixes all that.
The Xploderz Water Pellet Gun uses "little non-toxic balls of a superabsorbent polymer made of acrylic acid, sodium hydroxide, coloring and water." You simply soak them in warm water for four hours to get them plumped up and ready to shoot, and you're all set. And since the material was initially designed to help crops absorb and store water, there's no need to pick up after yourself once you've had your epic battles.
They also don't hurt as much as paintballs do, which could be a good thing or a bad thing depending on how sadistic you are. But either way, these things look pretty fun.